Decoding FLEX pagers using RTL-SDR and Linux

Superkuh2 demonstrates how to decode FLEX pager radio traffic. He uses gr-pager and zarya’s implementation of it on the Linux platform with the RTL-SDR dongle.

This script runs at a 250 KS/s sample rate and decodes one 12.5 KHz channel only. Internally it uses gnuradio’s optfir to generate low pass taps stopping at 12.5 KHz to use witih a frequency xlating FIR filter. It then passes what’s left to gr-pager’s flex_demod.

Here I show such an activity with the osmocom gr-fosphor visualization tacked on to patchvonbraun’s gnuradio multimode receiver for context.

For more detail on this process, visit SuperKuh’s website.

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  1. PDW is really nice, I agree. I just couldn’t get the audio piping to it working on linux under Wine. zarya’s script decodes only one channel at a time like PDW but there are other gr-osmocom + gr-pager gnuradio scripts that decode all FLEX channels in the band at once, like mothran’s FLEX_hackrf. There should be a version of these adapted for the max rtl-sdr bandwidth soon.

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